Method for continuous production of biodegradable aliphatic/aromatic polyester copolymer

ABSTRACT

A continuous preparation method of a biodegradable aliphatic/aromatic polyester copolymer includes: performing a first esterification reaction of an aliphatic dihydroxy compound with an aliphatic dicarboxylic acid at a temperature of 185° C. or less; continuously performing a second esterification reaction of a reaction product from the first esterification reaction; continuously performing a first polycondensation reaction of a reaction product from the second esterification reaction to obtain a prepolymer; continuously performing a second polycondensation reaction of the prepolymer to obtain a second polycondensation reaction product having an intrinsic viscosity from about 0.9 dl/g to about 1.0 dl/g; and continuously performing a third polycondensation reaction of the second polycondensation reaction product to prepare the biodegradable aliphatic/aromatic polyester copolymer, wherein the performing of the first esterification reaction or the continuously performing of the second esterification reaction includes adding an aromatic carboxylic acid. The biodegradable aliphatic/aromatic polyester copolymer prepared by control of the intrinsic viscosity of the second polycondensation reaction product may be improved in processibility, film formability, tensile/tearing strength, and blending ability with another polymer resin. Use of a less amount of the aliphatic dihydroxy compound as a starting material may reduce manufacturing costs.

TECHNICAL FIELD

The present invention relates to a continuous preparation method of abiodegradable aliphatic/aromatic polyester copolymer, and moreparticularly, to a method of continuously preparing a biodegradablealiphatic/aromatic polyester copolymer by using an aliphaticdicarboxylic acid, an aromatic dicarboxylic acid, and an aliphaticdihydroxy compound.

BACKGROUND ART

With recognition of conventional non-degradable plastics, such as nylon,polyethylene terephthalate, polypropylene, and polyethylene, as aprimary cause of environmental pollutions, biodegradable polyesters havebeen on the spotlight for environmental protection purposes.Biodegradable polyesters may be prepared by a batch production method ora continuous production method.

In the batch production method, a relatively long time that a reactionmixture spends in a reactor at a high temperature is needed to achievean intrinsic viscosity and a molecular weight of a target polyester; apartially heterogeneous reaction may occur even in the reactor; andphysical properties of the polyester may be changed at the initial,intermediate, and latter stages of a discharge process even after thecompletion of the reaction. In this regard, when a biodegradablepolyester spends at a high temperature for a long period of time, thebiodegradable polyester may be hydrolyzed by heat, which may affectmechanical strength and hydrolysis-resistant properties of thebiodegradable polyester and may cause a difference in quality due to thepartially heterogeneous reactions and different discharge times.

Meanwhile, the continuous production method may suppress the hydrolysisof biodegradable polyesters caused by heat generated in the batchproduction method. The continuous production method is appropriate formass production and to continuously obtain products with a uniformquality.

In general, diols such as 1,4-butanediol may be used as aliphaticdihydroxy compounds to prepare biodegradable polyesters. However,1,4-butanediol may be changed into tetrahydrofuran during a reaction,frequently causing troubles in a vacuum line of a manufacturing system.Furthermore, such 1,4-butanediol is required in excess amount.Therefore, there are needs for improvements in this regard.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention provides a method of continuously preparing abiodegradable aliphatic/aromatic polyester copolymer

Technical Solution

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of the present invention, there is provided acontinuous preparation method of a biodegradable aliphatic/aromaticpolyester copolymer, the method including: performing a firstesterification reaction of an aliphatic dihydroxy compound with analiphatic dicarboxylic acid at a temperature of 185° C. or less;continuously performing a second esterification reaction of a reactionproduct from the first esterification reaction; continuously performinga first polycondensation reaction of a reaction product from the secondesterification reaction to obtain a prepolymer; continuously performinga second polycondensation reaction of the prepolymer to obtain a secondpolycondensation reaction product having an intrinsic viscosity fromabout 0.9 dl/g to about 1.0 dl/g; and continuously performing a thirdpolycondensation reaction of the second polycondensation reactionproduct to prepare the biodegradable aliphatic/aromatic polyestercopolymer, wherein the performing of the first esterification reactionor the continuously performing of the second esterification reactionincludes adding an aromatic carboxylic acid.

Advantageous Effects

According to the one or more embodiments of the present invention, abiodegradable aliphatic/aromatic polyester copolymer improved inprocessibility, film formability, tensile/tearing strength, and blendingability with another polymer resin may be obtained by adjustment of theintrinsic viscosity of a second polycondensation reaction product. Aless amount of 1,4-butanediol than that used in conventional methods maybe used due to suppressed side reaction thereof, and consequentially anamount of 1,4-butanediol further added during preparation may also bereduced. Thus, manufacturing costs of the biodegradablealiphatic/aromatic polyester copolymer may be reduced. In addition,reduced emission of THF may be good for environmental protection.Therefore, the biodegradable aliphatic polyester may be prepared throughcontinuous processes at a mass scale.

MODE OF THE INVENTION

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

According to an aspect of the present invention, a continuouspreparation method of a biodegradable aliphatic/aromatic polyestercopolymer includes: performing a first esterification reaction of analiphatic dihydroxy compound with an aliphatic dicarboxylic acid at atemperature of 185° C. or less; continuously performing a secondesterification reaction of a reaction product from the firstesterification reaction; continuously performing a firstpolycondensation reaction of a reaction product from the secondesterification reaction to obtain a prepolymer, continuously performinga second polycondensation reaction of the prepolymer to obtain a secondpolycondensation reaction product having an intrinsic viscosity fromabout 0.9 dl/g to about 1.0 dl/g, and continuously performing a thirdpolycondensation reaction of the second polycondensation reactionproduct. The performing of the first esterification reaction or thecontinuously performing of the second esterification reaction mayinclude adding an aromatic dicarboxylic acid.

When the second polycondensation reaction product has an intrinsicviscosity less than 0.9 dl/g, reaction conditions for the secondpolycondensation reaction may need to be varied, for example, toincrease a time that a reaction mixture spends in a reactor for thesecond polycondensation reactions (hereinafter, referred to as areaction mixture residence time), a reaction temperature, and a stirringrate. On the other hand, when the second polycondensation reactionproduct has an intrinsic viscosity larger than 1.0 dl/g,depolymerization may also occur during the third polycondensationreaction, thus resulting in a biodegradable aliphatic/aromatic polyestercopolymer with a higher acid value and poor color characteristics.

To control the intrinsic viscosity of the second polycondensationreaction product within the above range, reaction conditions for thefirst esterification reaction, the second esterification reaction, thefirst polycondensation reaction, and the second polycondensationreaction, for example, in terms of polycondensation temperature,reaction mixture residence time, degree of vacuum, and flow rate, arevery important. These reaction conductions will be described later ingreater detail.

The reaction product from the continuous third polycondensationreaction, i.e., the biodegradable aliphatic/aromatic polyestercopolymer, may have an intrinsic viscosity from 1.4 dl/g to about 1.9dl/g.

When the intrinsic viscosity of the biodegradable aliphatic/aromaticpolyester copolymer is within this range, the biodegradablealiphatic/aromatic polyester copolymer may be improved inprocessibility, film formability, tensile/tearing strength, and blendingability with another polymer resin.

To control the intrinsic viscosity of the third polycondensationreaction product within the above range, reaction conditions for thethird polycondensation reaction, for example, in terms of reactiontemperature, reaction mixture residence time, degree of vacuum, and flowrate, are very important. These reaction conditions will be describedlater in greater detail.

In the performing of the first esterification reaction or thecontinuously performing of the second esterification reaction, anaromatic carboxylic acid may be added.

The term “esterification reaction” used herein refers to not only anesterification reaction of a dihydroxy compound with dicarboxylic acid,but also a trans-esterification reaction thereof.

As described above, esterification reaction may include a firstesterification reaction performed at a temperature of 185° C. or less toobtain an aliphatic oligomer, and a second esterification reactionperformed at a temperature from about 220 to about 250° C. to obtain analiphatic/aromatic oligomer.

The first esterification reaction of the aliphatic dihydroxy compoundwith aliphatic dicarboxylic acid is performed at a temperature of 185°C. or less to effectively inhibit a side reaction by which the aliphaticdihydroxy compound, for example, 1,4-butanediol, as a starting material,may be converted into tetrahydrofuran (THF).

The conversion of 1,4-butanediol to THF may highly occur at atemperature of about 190° C. or higher under acidic conditions. Thereaction temperature of the first esterification reaction may beadjusted to 185° C. or less to inhibit and minimize the conversion of1,4-butanediol into THF as much as possible. Thus, the amount of1,4-butanediol required for preparing the biodegradablealiphatic/aromatic polyester copolymer is significantly reduced comparedto conventional methods, and consequentially manufacturing costs of thebiodegradable polyester are reduced.

The disclosed method is suitable for environmental protection purposesbecause generation of a byproduct such as THF is inhibited, therebyreducing troubles in a vacuum line of a manufacturing system caused bythe byproduct, and consequentially improving workability andmanufacturing efficiency.

The reaction temperature of the first esterification reaction may be inthe range of about 160 to about 185° C., for example, about 180° C.

The first esterification reaction may be performed in a batch reactor.In some other embodiments, the first esterification reaction may beperformed as a continuous process while providing a mixture of thealiphatic dihydroxy compound and aliphatic dicarboxylic acid to thefirst esterification reactor.

To catalyze the first esterification reaction of the aliphatic dihydroxycompound with aliphatic dicarboxylic acid, a catalyst may be added intothe mixture of the aliphatic dihydroxy compound and aliphaticdicarboxylic acid.

The second esterification reaction, which is an esterification reactionof the aromatic dicarboxylic acid and the aliphatic oligomer obtainedfrom the first esterification reaction, may be performed at atemperature from about 220° C. to about 250° C. that is higher than thetemperature of the first esterification reaction, to obtain a targetproduct.

Examples of the aliphatic dihydroxy compound may include C2-C30alkanediol, such as ethanediol, 1,2-propanediol, 1,3-propanediol,1,2-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,2,4-dimethyl-2-ethyl-1,3-hexanediol, 2,2-dimethyl-1,3-propanediol,2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol,2,2,4-trimethyl-1,6-hexanediol, or a mixture thereof.

Examples of the aliphatic dicarboxylic acid may include a C2-C30aliphatic acid, for example, a C4-C14 aliphatic acid and derivativesthereof, which may be a linear or a branched acid.

An example of the aliphatic dicarboxylic acid may be a C7-C30cycloaliphatic dicarboxylic acid.

Examples of the aliphatic dicarboxylic acid may include malonic acid,succinic acid, glutaric acid, 2-methylglutaric acid, 3-methylglutaricacid, adipic acid, pimellic acid, suberic acid, azelaic acid, sebacicacid, undecanedioic acid, dodecanedioic acid, brassylic acid,tetradecanedioic acid, furmaric acid, 2,2-dimethylglutaric acid, maleicacid, itaconic acid, or a mixture thereof.

Examples of the aromatic dicarboxylic acid may include a C8-C30 aromaticdicarboxylic acid, such as terephthalic acid, isophthalic acid,2,6-naphthoic acid, 1,5-naphthoic acid, or a mixture thereof.

A total amount of the aliphatic dihydroxy compound used in the firstesterification reaction and second esterification reaction may be in arange of about 1.1 to about 1.5 moles based on 1 mole of a total amountof the aliphatic dicarboxylic acid and the aromatic dicarboxylic acid.Thus, a production yield of the oligomer may be high even with the useof a smaller amount of the aliphatic dihyroxy compound compared toconventional methods in which an amount of the aliphatic dihydroxycompound used is 2 moles or more based on 1 mole of a total amount ofaliphatic dicarboxylic acid and aromatic dicarboxylic acid.

In the first esterification reaction, an amount of used aliphaticdicarboxylic acid may be from about 30 mol % to about 99 mol % based ona total mole of dicarboxylic acid.

An amount of the used aromatic dicarboxylic acid may be in a range ofabout 1 mol % to about 70 mol % based on a total mole of the useddicarboxylic acid. A total amount of aliphatic dicarboxylic acid andaromatic dicarboxylic acid is set to be 100 mol %. In the mixture of thealiphatic dihydroxy compound and aliphatic dicarboxylic acid, at leastone selected from a catalyst, a heat stabilizer, a branching agent, acolor stabilizing agent, and a color control agent may be further addedthereto.

An example of the catalyst may be a compound at least one metal selectedfrom lithium, magnesium, calcium, barium, cerium, titanium, zirconium,hafnium, vanadium, manganese, iron, cobalt, iridium, nickel, zinc, andtin.

Examples of the metal-containing compound may include a metal organicacid salt, a metal alkoxide, a metal complex, a metal oxide, a metalhydroxide, a metal carbonate, a metal phosphate, a metal sulfate, ametal nitrate, or a metal chloride.

An example of the catalyst may be tetra-n-butyl titanate ortetra-n-isopropyl titanate.

The catalyst may be used in an amount in a range of about 0.00001 toabout 0.2 moles based on 1 mole of dicarboxylic acid. When the amount ofthe catalyst used is within this range, a yield of the product of thefirst esterification reaction may be high. When the amount of thecatalyst is less than about 0.00001 mole, the reaction rate may be low.On the other hand, when the amount of the catalyst used is more thanabout 0.2 mole, a rate of depolymerization may be accelerated in the endof polycondensation reaction, and thus failing to achieve a targetdegree of polymerization may not be obtained, and resulting in reducedtensile strength/internal tearing strength, and reduced chromaticity.

As the branching agent, a compound including at least three groups foresterification selected from a carboxyl group, a hydroxyl group, and anamine group may be used. Examples of the branching agent may includetrimellitic acid, citric acid, maleic acid, glycerol, monosaccharide,disaccharide, dextrin, or a reduced sugar.

When the branching agent is used, the biodegradable polyester copolymerof a high molecular weight may be easily prepared, but due to a widedistribution of molecular weights, the tensile strength/internal tearingstrength may be reduced. Accordingly, the amount of the branching agentmay be appropriately controlled in this regard.

The amount of the branching agent may be in the range of about 0.00001to about 0.2 mole based on 1 mole of dicarboxylic acid. When the amountof the branching agent is within this range, a biodegradablealiphatic/aromatic polyester copolymer having a high molecular weightwith improved tensile strength/internal tearing strength may beobtained.

Examples of the color stabilizing agent may include phosphoric acid,phosphorous acid, triphenylphosphite, triphenylphosphate,trimethylphosphate, triethylphosphate, sodium hypophosphite, or sodiumphosphonate. An amount of the color stabilizing agent may be in therange of about 0.00001 to about 0.2 mole based on 1 mole of dicarboxylicacid.

An example of the color control agent may be cobalt acetate.

The first polycondensation reaction (also referred to as apre-polycondensation) of a reaction product obtained from the secondesterification reaction may be continuously performed to obtain aprepolymer.

A catalyst may be further added into the reaction mixture to catalyzethe first polycondensation reaction. In some embodiments, at least oneselected from a catalyst and a stabilizer may be further added into thereaction mixture.

The step of continuously performing polycondensation reaction of theprepolymer obtained from the first polycondensation reaction may beperformed in multiple steps. For example, the multiples steps mayinclude continuously performing the second polycondensation reaction ofthe prepolymer and continuously performing the third polycondensationreaction of the product obtained from the second polycondensationreaction.

In regard to the method of the present invention, even when no or asmall amount of a chain extender is used, a target biodegradablealiphatic/aromatic polyester copolymer having a large molecular weightmay be prepared.

According to embodiments of the present invention, the biodegradablealiphatic/aromatic polyester copolymer may include a first repeat unitrepresented by Formula 1 and a second repeat unit represented by Formula2. A weight average molecular weight of the copolymer may be, forexample, in a range of about 120,000 to about 170,000.

In Formula 1, R1 and R2 may be each independently a divalent C1-C30aliphatic hydrocarbon group.

In Formula 2, R3 may be a divalent C6-C30 aromatic hydrocarbon group,and R4 may be a divalent C1-C30 aliphatic hydrocarbon group.

The copolymer may be an alternating copolymer, a random copolymer, or ablock copolymer.

In Formula 1, R1 and R2 may be each independently ethylene, propylene,or butylene. In Formula 2, R3 may be a phenylene group, and R4 may beethylene, propylene, or butylene.

The aliphatic/aromatic polyester copolymer may be a polymer having afirst repeat unit represented by Formula 3 and a second repeat unitrepresented by Formula 4.

A molar ratio of the first repeat unit and the second repeat unit may becontrolled by varying the amount of the aliphatic dicarboxylic acid andthe amount of the aromatic dicarboxylic acid, which are reacted with thealiphatic dihydroxy compound as described above.

The molar ratio of the first repeat unit and the second repeat unit maybe in the range of about 30:70 to about 99:1

In Formulas 1 and 2, the aliphatic hydrocarbon may be a C1-C30 alkylenegroup, a C5-C30 cycloalkylene group, or a C4-C30 cycloheteroalkylenegroup.

In Formula 2, the aromatic hydrocarbon may be a C6-C30 arylene group ora C5-C30 heteroarylene group.

Embodiments of the method of preparing a biodegradablealiphatic/aromatic polyester copolymer will now be described in moredetail. A first esterification reaction may be continuously performed inan esterification reactor.

First, an aliphatic dihydroxy compound and an aliphatic dicarboxylicacid may be mixed in a first slurry tank to prepare a slurry.

A catalyst may be further added into the slurry.

[First Continuous Esterification Reaction]

The slurry obtained from the first slurry tank may be continuously addedinto a first esterification reactor to perform esterification reactionof the aliphatic dihydroxy compound and the aliphatic dicarboxylic acid,at a temperature of 185° C. or less, for example, a temperature in therange of about 160 to about 185° C. A flow rate of the slurry added intothe first esterification reactor may be adjusted according to a size ofthe reactor to control a residence time of a reaction mixture in thereactor, but the flow rate is not limited to a specific range. Forexample, when a volume of the first esterification reactor is about 0.49m3, the flow rate of the slurry may be in a range of about 20 to about40 kg/h.

The catalyst may be further added into the first esterification reactor.

The pressure in the first esterification reactor may be controlled in anormal pressure range, and the term “normal pressure” used herein mayrefer to a range of about 760±10 torr.

The heat stabilizer may be further added into the reaction mixture.

A level of the reaction mixture (i.e., a quantity of the reactionmixture filled in the reactor) and a flow rate thereof may be adjustedsuch that a time spent by the reaction mixture in the firstesterification reactor is from 2 hours to 6 hours.

Water produced as a byproduct from the esterification reaction may beremoved through a condenser.

An acid value of the aliphatic oligomer obtained from the firstesterification reaction may be less than 1 mg KOH/g or less, and forexample, may be in a range of about 0.1 to about 1 mg KOH/g. A weightaverage molecular weight of the aliphatic oligomer may be in a range ofabout 300 to about 1,000.

The reaction mixture in the first esterification reactor may becontinuously added into a second slurry tank at a flow rate from about20 kg/h to about 40 kg/h. After adding the aromatic dicarboxylic acidinto the second slurry tank, the mixture may be stirred.

As a reactor for the first esterification reaction, a reactor suitablefor manufacturing an ester oligomer having a molecular weight within theabove range, and flow characteristics corresponding to the molecularweight, for example, in terms of viscosity and melting index, may beused. Such reactors are widely known in the field of polyester polymersynthesis to which the present invention pertains. For example, avertical-type reactor equipped with a stirrer having pitched paddleimpellers (manufactured by Hado, Korea) may be used. The stirrer mayform a resultant flow of a under flow and an axial flow to make an idealflow pattern resulting in a high stirring effect (refer tohttp://www.hado.co.kr/default1.html).

[Second Esterification Reaction]

The slurry in the second slurry tank may be continuously added into asecond esterification reactor to perform a second esterificationreaction of the aliphatic oligomer and terephthalic acid at atemperature in a range of about 220 to about 250° C. The reactionpressure may be normal. When the second esterification reactor has avolume of about 0.4 m3, the flow rate may be from about 30 kg/h to about45 kg/h.

Water produced from the ester reaction may be removed through acondenser.

To compensate for 1,4-butanediol (BDO) that is converted intotetrahydrofuran (THF) or lost by being distilled at a high temperature,an aliphatic dihydroxy compound such as pure BDO may be furthercontinuously added into the second esterification reactor, for example,having a volume of about 0.4 m3 via a separate injection device at aflow rate in a range of about 0.1 to about 8 kg/h for reaction.

The residence time of the reaction mixture in the second esterificationreactor may be adjusted to be from about 2 to about 6 hours bycontrolling the level and the flow rate of the reaction mixture.

According to the above-described embodiments of the preparation method,the amount of THF removed via the condenser may be reduced, and thus theamount of pure BDO added via an injection device may also besignificantly reduced compared to conventional methods.

A reaction product resulting from the second esterification reaction mayhave an acid value from about 10 mg KOH/g to about 40 mg KOH/g and aweight average molecular weight from about 1,000 to about 5,000.

As a reactor for the second esterification, a reactor suitable formanufacturing an ester oligomer having a molecular weight within theabove range, and flow characteristics corresponding to the molecularweight, for example, in terms of viscosity and melting index, may beused. Such reactors are widely known in the field of polyester polymersynthesis to which the present invention pertains. For example, the sametype of reactor as that used in the first esterification reaction may beused.

[First Polycondensation Reaction]

The reaction product obtained from the second esterification reactionmay be continuously added into the first polycondensation reactor, andthen a first polycondensation (i.e., pre-polymerization) of the reactionproduct may be performed to obtain a prepolymer. The reactiontemperature may be in a range of about 220 to about 250° C., and thedegree of vacuum may be in a range of about 10 to about 50 torr.

At least one selected from a catalyst and a heat stabilizer may befurther added into the reactor to catalyze the reaction.

A level of the reaction mixture (i.e., a quantity of the reactionmixture filled in the reactor) and a flow rate thereof may be adjustedsuch that a time spent by the reaction mixture in the firstpolycondensation reactor is 1.5 to 3 hours.

The prepolymer as the reaction product from the first polycondensationreaction may have an acid value from about 5 mg KOH/g to about 10 mgKOH/g and a weight average molecular weight from about 6,900 to about14,000.

As a reactor for the first polycondensation reaction, a reactor suitablefor manufacturing a prepolymer having a molecular weight within theabove range and viscosity corresponding to the molecular weight may beused. Such reactors are widely known in the field of polyester polymersynthesis to which the present invention pertains. For example, avertical-type reactor (manufactured by Hitachi Plant Technology)equipped with an anchor-type stirrer may be used. When the firstpolycondensation reactor has a volume of about 0.4 m3, the flow rate maybe in the range of about 20 kg/h to about 50 kg/h.

To control the intrinsic viscosities of the reaction products from thesecond polycondensation reaction and the third polycondensationreaction, reaction conditions for these reactions, for example, in termsof reaction mixture residence time (i.e., the time spend by eachreaction mixture in the corresponding reactor), reaction temperature,and degree of vacuum, are very important.

[Second Polycondensation Reaction]

The prepolymer obtained from the first polycondensation reaction may becontinuously added into the second polycondensation reactor, and then asecond polycondensation reaction of the prepolymer may be performed at atemperature of about 220 to about 250° C. The degree of vacuum may be inthe range of about 2 to about 7 torr, and the residence time of thereaction mixture may be adjusted to be in the range of about 1.5 toabout 3 hours by controlling the level of the reaction mixture (i.e., aquantity of the reaction mixture filled in the reactor) and the flowrate thereof.

The reaction product from the second polycondensation reaction may havean acid value in a range of about 3 to 8 mg KOH/g, a weight averagemolecular weight in a range of about 50,000 to about 80,000, a meltingindex in a range of about 15 to about 25 g/10 min, and an intrinsicviscosity in a range of about 0.9 to about 1.0 dl/g. Using the reactionproduct from the second polycondensation reaction having an intrinsicviscosity within this range, the resulting biodegradablealiphatic/aromatic polyester copolymer may be improved in colorcharacteristics and yield.

As a reactor for the second polycondensation reaction, a reactorsuitable for manufacturing a prepolymer having a molecular weight withinthe above range, and flow characteristics corresponding to the molecularweight, for example, in terms of viscosity and melting index, may beused. Such reactors are widely known in the field of polyester polymersynthesis to which the present invention pertains. For example, ahorizontal-type reactor (manufactured by Hitachi Plant Technology)equipped with a horizontally arranged single stirrer may be used. Whenthe second polycondensation horizontal-type reactor has a volume ofabout 0.24 m3, the flow rate may be in a range of about 20 to about 40kg/h, and the number of revolutions of the stirrer may be in a range ofabout 1.5 to about 8 rpm.

[Third Polycondensation Reaction]

The reaction product obtained from the second polycondensation reactionmay be continuously added into the third polycondensation reactor, andthen a third polycondensation reaction may be performed at a temperatureof about 220 to about 250° C. In this regard, the degree of vacuum maybe in the range of about 0.5 to about 2 torr.

A level of the reaction mixture (i.e., a quantity of the reactionmixture filled in the reactor) and the flow rate thereof may be adjustedsuch that a time spent by the reaction mixture in the thirdpolycondensation reactor is 1 to 3 hours.

A final polymer after completion of the reaction may be passed through acooling water bath to be cooled down to solidify, cut into a desiredform with a cutter, dried, and then transferred into a silo, therebyresulting in a target biodegradable aliphatic polyester. In someembodiments, the final polymer may be solidified with cool water in anunder-water pelletizer prior to the cutting.

The polyester copolymer may have an acid value from about 1.5 to about 6mg KOH/g, a weight average molecular weight from about 120,000 to about170,000, an intrinsic viscosity from about 1.4 to about 1.9 dl/g, and amelting index from about 2 g to about 5 g per 10 minutes.

As a reactor for the third polycondensation reaction, a reactor suitablefor manufacturing a prepolymer having a molecular weight within theabove range, and flow characteristics corresponding to the molecularweight, for example, in terms of viscosity and melt index, may be used.Such reactors are widely known in the field of polyester polymersynthesis to which the present invention pertains. For example, ahorizontal-type polycondensation reactor (manufactured by Hitachi PlantTechnology) equipped with two horizontally arranged stirrers may beused. In some embodiments, the third horizontal-type polycondensationreactor of the Hitachi Plant Technology may have two spectacle-shapedblades horizontally arranged parallel to each other. Here, a bladeconnected to each rotation axis passes through between the blade andanother blade of another rotation axis to widen a surface area of highviscosity reaction mixture and induce an efficient reaction (refer tohttp://www.hitachi-pt.com/product/ip/element_technology/simulation.html).

When the third polycondensation reactor has a volume of about 0.192 m3,the flow rate may be from about 20 kg/h to about 40 kg/h, and the numberof revolutions of the stirrer may be from about 5 rpm to about 8 rpm.

During the first, second, and third polycondensation reactions, a colorstabilizing agent may be further added into each of the reactors for thepolycondensation reactions.

Examples of the color stabilizing agent may be phosphoric acid,phosphorous acid, triphenyl phosphite, triphenyl phosphate, sodiumhypophosphite, and sodium phosphonate.

Hereinafter, a method of preparing a biodegradable aliphatic/aromaticpolyester copolymer according to another embodiment of the presentinvention will now be described in more detail.

According to another embodiment of the present invention, a firstesterification reaction may be performed in a batch reactor, unlike themethods according to the above-described embodiments. This method willbe described in detail below.

In the batch reactor, esterification reaction of an aliphatic dihydroxycompound and aliphatic dicarboxylic acid may be performed at atemperature of 185° C. or less to obtain an aliphatic oligomer.

The esterification reaction may be performed in the presence of acatalyst.

Water produced by the esterification reaction may be removed through acondenser, and a heat stabilizer may be further added into the batchreactor.

The aliphatic oligomer may be stored in a storage tank.

The aliphatic oligomer in the storage tank and the aromatic dicarboxylicacid may be supplied into a first slurry tank. In this regard, thearomatic dicarboxylic acid may be quantified in a hopper and put intothe first slurry tank. The aliphatic oligomer may be stirred while theinternal temperature of the first slurry tank is maintained in a rangefrom about 70 to about 80° C.

In some other embodiments, the aromatic dicarboxylic acid may not besupplied into the first slurry tank. Instead, the aromatic dicarboxylicacid may be added into the reactor during the esterification reaction ofthe aliphatic dihydroxy compound and aliphatic dicarboxylic acid.

The slurry obtained in the first slurry tank may be continuously flowedinto the second slurry tank. An internal temperature of the secondslurry tank may be maintained in a range from about 70 to about 80° C.to ensure continuous supply of the slurry into the second esterificationreactor at a stable flow rate.

While the slurry manufactured in the second slurry tank is continuouslyinput into the second esterification reactor, the second esterificationreaction of the aliphatic oligomer and the aromatic dicarboxylic acidmay be performed. A description of the subsequent reactions, which arethe same as in the above-described embodiments, will be omitted here.

According to an embodiment, the biodegradable aliphatic/aromaticpolyester copolymer may be used as a film, a sheet, a fiber, or othermolded material.

One or more embodiments of the present invention will now be describedin detail with reference to the following examples. However, theseexamples are not intended to limit the scope of the one or moreembodiments of the present invention.

Test Method

First, the intrinsic viscosities, acid values, weight average molecularweights of the reaction products obtained in each step of Examples 1 to5 below were evaluated as follows.

(1) Intrinsic Viscosity (I.V.)

Phenol and 1,2-dichlorobenzene were mixed in a weight ratio of about 5:5to prepare a reagent. 0.25 g of pellets (sample) was put into 25 mL ofthe reagent and completely dissolved at about 80° C. to obtain asolution, which was transferred into a Ubbelohde viscosity and then keptin a 25° C. thermostatic bath for about 10 minutes, followed by countingdrop seconds of the solution with a viscometer and an aspirator. Dropseconds of the solvent were counted in the same method. A relativeviscosity (R.V) and an intrinsic viscosity (I.V) of the solution werecallused using Equations 1 and 2 below, where C indicates aconcentration of a sample.

R.V.=Drop seconds of sample/Drop seconds of solvent  [Equation 1]

I.V.=1/4(R.V−1)/C+3/4(ln R.V/C)  [Equation 2]

(2) Acid Value

The acid value was measured according to DIN EN 12634, and the solventwas a mixture of 10 parts by volume of N,N-dimethylsulfoxide, 8 parts byvolume of propane-2-ol, and 7 parts by volume of toluene.

A sample was heated to a temperature of 50° C., a single-rod electrodewas used in a circuit, and a container containing the sample was filledwith potassium chloride. A standard solution used herein was tetramethylammonium hydroxide (TMAH).

(3) Weight Average Molecular Weight

The weight average molecular weight was measured by gel permeationchromatography (GPC, manufactured by Agilent HP 1100), and polystyrenewas used as a standard material. A column was prepared by continuouslyconnecting a PLgel (5 urn) Mixed-D (manufactured by Phenomenex Company)and a PLgel (10 um) Mixed-B. The measurement was performed underconditions in which a temperature of the column and the detector was 35°C. and the flow rate was 1 ml/min.

Example 1 Preparation of Biodegradable Poly(ButyleneAdipate-Co-Terephthalate) (PBAT)

[First Slurry Tank]

1,4-butanediol and adipic acid were put into a first slurry tank in amolar ratio of 1.3:0.52, stirred at a temperature of 70° C., and mixedto prepare a slurry.

[First Esterification Reaction]

The slurry from the first slurry tank was continuously put into a firstesterification reactor for first esterification reaction of1,4-butanediol and adipic acid. The flow rate was about 35 kg/h, thereaction temperature was 180° C., and the pressure was normal.

A vertical-type reactor equipped with a stirrer having pitched paddleimpellers (manufactured by Hado, Ltd., Korea) was used as the firstesterification reactor for the first esterification reaction (refer tohttp://www.hado.co.kr/default1.html). Triphenyl phosphate andtetra-n-butyl titanate were added into a reaction mixture in the firstesterification reactor.

Triphenyl phosphate and tetra-n-butyl titanate were each pre-mixed with1,4-butanediol to a concentration of 10% by weight and were continuouslyadded into the first esterification reactor. The flow rate wascontrolled to use 0.1 g (3.06×10−4 mol) of triphenyl phosphate and 0.3 g(8.815×10−4 mol) of adipic acid, each per 0.52 moles of the adipic acid.

Water produced from the esterification reaction was removed through acondenser.

A level of the reaction mixture, i.e., a quantity of the reactionmixture filled in the reactor, was adjusted such that a time spent bythe reaction mixture in the first esterification reactor was 3 hours.

A reaction product from the first esterification reaction had an acidvalue of about 1 mg KOH/g, and a weight average molecular weight ofabout 800.

[Second Slurry Tank]

The reaction mixture from the first esterification reactor wascontinuously put into a second slurry tank at a flow rate of about 30kg/h, followed by adding terephthalic acid thereinto and mixing togetherwith stirring to prepare a slurry. A final molar ratio of1,4-butanediol, adipic acid, and terephthalic acid in thereaction\slurry was adjusted to about 1.3:0.52:0.48.

[Second Esterification Reaction]

The slurry from the second slurry tank was continuously put into asecond esterification reactor for second esterification reaction of analiphatic oligomer as a product from the first esterification reactionwith terephthalic acid. The flow rate was 40 kg/h, the reactiontemperature was 230° C., and the pressure was normal.

The same reactor as used in the first esterification reaction was usedfor the second esterification reaction.

Water produced from the second esterification reaction was removedthrough a condenser, followed by continuously adding pure 1,4-butanediolinto the reactor at a flow rate of 2 kg/h for reaction. A level of thereaction mixture, i.e., a quantity of the reaction mixture filled in thereactor, was adjusted such that a time spent by the reaction mixture inthe reactor was to 3.5 hours.

A reaction product from the second esterification reaction had an acidvalue of about 20 mg KOH/g, and a weight average molecular weight ofabout 2,000.

[First Polycondensation Reaction]

The reaction product from the second esterification reaction wascontinuously put into a first polycondensation reactor for firstpolycondensation (referred to as pre-polymerization) to obtain apre-polymer. The flow rate was 35 kg/h, the reaction temperature was240° C., and the degree of vacuum was 20 torr.

A vertical-type reactor (manufactured by Hitachi Plant Technology)equipped with an anchor-type stirrer was used as the firstpolycondensation reactor.

Tetra-n-butyl titanate as a catalyst was pre-mixed with 1,4-butanediolto a concentration of 10% by weight, and was continuously added into thefirst polycondensation reactor. The flow rate was adjusted to use 0.3 g(8.815×10−4 mol) of tetra-n-butyl titanate per 0.52 moles of adipicacid.

A level of the reaction mixture, i.e., a quantity of the reactionmixture filled in the reactor, was adjusted such that a time spent bythe reaction mixture in the reactor was 2 hours.

A reaction product form the first polycondensation reaction had an acidvalue of about 7 mg KOH/g and a weight average molecular weight of about8,000.

[Second Polycondensation Reaction]

The reaction product from the first polycondensation reaction wascontinuously put into a second polycondensation reactor for secondpolycondensation reaction. The flow rate was 35 kg/h, the reactiontemperature was 240° C., and the degree of vacuum was 6 torr. A level ofthe reaction mixture, i.e., a quantity of the reaction mixture filled inthe reactor, was adjusted such that a time spent by the reaction mixturein the reactor was 2 hours. A horizontal-type reactor (manufactured byHitachi Plant Technology) equipped with a horizontally arranged singlestirrer was used as the second polycondensation reactor. The number ofrevolutions of the single stirrer was about 5 rpm. The reaction productfrom the second polycondensation reaction had an acid value of about 5mg KOH/g, and a weight average molecular weight of about 80,000.

[Third Polycondensation Reaction]

The reaction product from the second polycondensation reaction wascontinuously put into a third polycondensation reactor for thirdpolycondensation reaction. The flow rate was 35 kg/h, the reactiontemperature was 240° C., and the degree of vacuum was 1 torr.

A horizontal-type reactor (manufactured by Hitachi Plant Technology)equipped with two horizontally arranged stirrers was used as the thirdpolycondensation reactor. The number of revolutions of the singlestirrer was about 5 rpm.

A level of the reaction mixture, i.e., a quantity of the reactionmixture filled in the reactor, was adjusted such that a time spent bythe reaction mixture in the third polycondensation reactor was 1.5hours.

A final polymer after completion of the third polycondensation reactionwas cooled down by being passed through a cooling water bath tosolidify. Then, the final polymer was cut with a cutter and dried toobtain poly(butylene adipate-co-terephthalate (PBAT) as a targetbiodegradable polyester copolymer including a repeat unit of1,4-butylene-adipate and another repeat unit of 1,4-butyleneterephthalate.

The resulting PBAT had an acid value of about 2.5 mg KOH/g and a weightaverage molecular weight of about 170,000.

The same reactors as the first esterification reactor, the secondesterification reactor, the first polycondensation reactor, the secondpolycondensation reactor, and the third polycondensation reactor used inExample 1 were used in Examples 2 to 5, which will be described below.

Example 2 Preparation of Biodegradable PBAT

[First Esterification Reaction]

1,4-butanediol and adipic acid were put into a batch reactor in a molarratio of 1.3:0.52, followed by esterification reaction at a temperatureof 180° C. at an atmospheric pressure to obtain bishydroxy butyleneadipate (hereinafter, referred to as BHBA), which was stored in astorage tank.

Water produced from the first esterification reaction was removedthrough a condenser, followed by continuously adding triphenyl phosphateand tetra-n-butyl titanate into a batch reactor for esterificationreaction of 1,4-butanediol with adipic acid. Triphenyl phosphate andtetra-n-butyl titanate were each pre-mixed with 1,4-butanediol to aconcentration of 10% by weight prior to the continuous adding into thebatch reactor. The amounts of triphenyl phosphate and tetra-n-butyltitanate were about 0.1 g and about 0.3 g, respectively, each per 0.52mol of adipic acid.

The reaction product from the first esterification reaction had an acidvalue of about 1 mg KOH/g and a weight average molecular weight of about700.

The BHBA prepared in the batch reactor was mixed with terephthalic acidin the first slurry tank to prepare a slurry. The terephthalic acid wasquantified in a hopper, added into the first slurry tank, and thenstirred while maintaining temperature at about 70° C. to 80° C. A molarratio of 1,4-butanediol, adipic acid, and terephthalic acid was adjustedto be 1.3:0.52:0.48.

The slurry prepared in the first slurry tank was continuously flowedinto the second slurry tank of which temperature was maintained at about75° C.

[Second Esterification Reaction]

The slurry prepared in the second slurry tank was continuously addedinto the second esterification reactor to react BHBA with terephthalicacid. The flow rate of the slurry was 40 kg/h, the reaction temperaturewas 230° C., and the pressure was normal.

Water produced from the second esterification reaction and THF generatedfrom a side reaction of 1,4-butanediol were removed through a condenser.Pure 1,4-butanediol was continuously added into the secondesterification reactor via an injection device at a flow rate of about2.5 kg/h for reaction. A level of the reaction mixture, i.e., a quantityof the reaction mixture filled in the reactor, was adjusted such that atime spent by the reaction mixture in the second esterification reactorwas 3.5 hours.

The reaction product from the second esterification reaction was about20 mg KOH/g and a weight average molecular weight of about 2,000.

[First Polycondensation Reaction]

The reaction product from the second esterification reaction wascontinuously added into the first polycondensation reactor for firstpolycondensation (referred to as pre-polymerization). The flow rate ofthe reaction product was 35 kg/h, the reaction temperature was 240° C.,and the degree of vacuum was 20 torr.

Tetra-n-butyl titanate was pre-mixed with 1,4-butanediol to aconcentration of 10% by weight, and then continuously added into thefirst polycondensation reactor via an injection device at a flow rate of0.84 kg/h. A level of the reaction mixture was adjusted such that a timespent by the reaction mixture in the first polycondensation reactor was2 hours.

The reaction product from the first polycondensation reaction had anacid value of about 7 mg KOH/g and a weight average molecular weight ofabout 9,500.

[Second Polycondensation Reaction]

The reaction product, i.e., pre-polymer, from the first polycondensationreaction was continuously added into the second polycondensation reactorfor second polycondensation reaction. The flow rate of the pre-polymerwas 35 kg/h, the reaction temperature was 240° C., and the degree ofvacuum was 6 torr.

A level of the reaction mixture, i.e., a quantity of the reactionmixture filled in the reactor, was adjusted such that a time spent bythe reaction mixture in the second polycondensation reactor was 2 hours.

The reaction product from the second polycondensation reaction had anacid value of about 4.2 mg KOH/g and a weight average molecular weightof about 76,000.

[Third Polycondensation Reaction]

The reaction product from the second polycondensation reaction wascontinuously added into the third polycondensation reactor for thirdpolycondensation reaction. The flow rate of the reaction product was 35kg/h, the reaction temperature was 240° C., and the degree of vacuum wasabout 1 torr.

A level of the reaction mixture, i.e., a quantity of the reactionmixture filled in the reactor, was adjusted such that a time spent bythe reaction mixture in the third polycondensation reactor was 1.5hours. A final polymer after completion of the third polycondensationreaction was cooled down by being passed through a cooling water bath tosolidify. The final polymer was cut with a cutter and dried to obtainbiodegradable polybutylene adipate-co-terephthalate (PBAT).

The PBAT had an acid value of about 2.7 mg KOH/g and a weight averagemolecular weight of about 155,000.

Example 3 Preparation of Biodegradable PBAT First Slurry Tank

1,4-butanediol, adipic acid, and terephthalic acid were put into thefirst slurry tank in a molar ratio of 1.3:0.52:0.48, stirred and mixedtogether at a temperature of 60° C. to prepare a slurry.

[First Esterification]

The slurry from the first slurry tank was continuously put into thefirst esterification reactor for first esterification reaction. The flowrate of the slurry was 48 kg/h, the reaction temperature was 180° C.,and the pressure was normal.

Triphenyl phosphate and tetra-n-butyl titanate were added into thereaction mixture in the first esterification reactor to performesterification reaction.

Triphenyl phosphate and tetra-n-butyl titanate were each pre-mixed with1,4-butanediol to a concentration of 10% by weight, and werecontinuously added into the first esterification reactor. The flow rateof the reaction mixture was adjusted to use 0.1 g (2.94×10−4 mol) oftetra-n-butyl titanate and 0.3 g (9.195×10−4 mol) of triphenylphosphate, each per 0.52 mol of adipic acid.

Water produced from the first esterification reaction was removedthrough a condenser.

[Second Esterification Reaction]

The reaction product from the first esterification reaction wascontinuously added into the second esterification reactor to react thereaction product with terephthalic acid. The flow rate of the reactionproduct was 40 kg/h, the reaction temperature was 230° C., and thepressure was normal.

Water produced from the second esterification reaction was removedthrough a condenser, followed by continuously adding pure 1,4-butanediolinto the second esterification reactor at a flow rate of 2.5 kg/h forreaction. A level of the reaction mixture, i.e., a quantity of thereaction mixture filled in the reactor, was adjusted such that a timespent by the reaction mixture in the second esterification reactor was3.5 hours.

The first polycondensation reaction, the second polycondensationreaction, and the third polycondensation reaction were performed in thesame manner as Example 1 to obtain a target PBAT as a biodegradablepolyester.

The PBAT had an acid value of about 2.1 mg KOH/g and a weight averagemolecular weight of about 145,000.

Example 4 Preparation of Biodegradable PBAT

PBAT as a biodegradable polyester was obtained in the same manner asExample 1, except that the first esterification reaction was performedat a temperature of 160° C., and a level of the reaction mixture, i.e.,a quantity of the reaction mixture spent in the reactor, was adjustedsuch that a time spent by the reaction mixture in the firstesterification reactor was 6 hours.

Example 5 Preparation of Biodegradable PBAT

PBAT as a biodegradable polyester was obtained in the same manner asExample 1, except that the first esterification reaction was performedat a temperature of 185° C., and a level of the reaction mixture, i.e.,a quantity of the reaction mixture filled in the reactor, was adjustedsuch that a time spent by the reaction mixture in the firstesterification reactor was 2.5 hours.

Reference Example 1 Preparation of Biodegradable PBAT

PBAT as a biodegradable polyester was obtained in the same manner as inExample 1, except that a level of the reaction mixture for the secondpolycondensation reaction, i.e., a quantity of the reaction mixturefilled in the second polymer condensation reactor, was adjusted suchthat a time spent by the reaction mixture in the second polycondensationreactor was about 3.5 hours.

Reference Example 2 Preparation of Biodegradable PBAT

PBAT as a biodegradable polyester was obtained in the same manner as inExample 1, except that a level of the reaction mixture for the secondpolycondensation reaction, i.e., a quantity of the reaction mixturefilled in the second polymer condensation reactor, was adjusted suchthat a time spent by the reaction mixture in the second polycondensationreactor was about 1 hour.

Evaluation Example 1 Intrinsic Viscosity

Intrinsic viscosities of the second polycondensation reaction products,and the third polycondensation reaction products (biodegradable PBATs)of Examples 1 to 5 and Reference Examples 1 and 2 were evaluated. Theevaluation results are shown in Table 1 below.

TABLE 1 Intrinsic viscosity of Intrinsic viscosity of secondpolycondensation biodegradable PBAT Example reaction product (dl/g)(dl/g) Example 1 1.0 1.9 Example 2 0.9 1.5 Example 3 0.9 1.4 Example 40.9 1.5 Example 5 1.0 1.7 Reference Example 1 1.3 1.1 Reference Example2 0.6 1.0

Referring to Table 1, the second polycondensation reaction products ofExamples 1 to 5 had an intrinsic viscosity from about 0.9 dl/g to about1.0 dl/g, and consequently the biodegradable PBATs obtained therefromhad an intrinsic viscosity from about 1.4 dl/g to about 1.9 dl/g.Meanwhile, the biodegradable PBAT of Reference Example 1, i.e., a thirdpolycondensation reaction product, had a intrinsic viscosity even lowercompared to the second polycondensation reaction product. Since thesecond polycondensation reaction product of Reference Example 2 had avery low intrinsic viscosity of about 0.6 dl/g, the thirdpolycondensation reaction product obtained from the secondpolycondensation reaction product had a very low intrinsic viscosity ofabout 1.0 dl/g,

Evaluation Example 2 Comparison of Amount of 1,4-Butanediol with that ofDicarboxylic Acid

The amounts of 1,4-butanediol used in preparing biodegradable PBATs inExamples 1 to 3 were compared to each other. The results are shown inTable 2 below.

TABLE 2 Moles of 1,4-butanediol based on 1 Example mol of dicarboxylicacid (mol) Example 1 1.45 Example 2 1.48 Example 3 1.48 ComparativeExample 1* 2.18 *The amount of 1,4-butanediol used in ComparativeExample 1, provided for comparison with Examples 1 to 3, was calculatedbased on a molar ratio disclosed in Example 1 of Korean Publication No.10-2011-007186.

Referring to Table 2, the amounts of 1,4-butanediol used foresterification in Examples 1 to 3 are found to be less than that used inComparative Example 1. This indicates that conversion reaction of1,4-butanediol into THF was suppressed during the esterification inExamples 1 to 3.

Evaluation Example 3 Comparison of Generated Amount of THF

The amounts of THF generated during the second esterification reactionof Examples 1 to 5 were measured per 1 mole of dicarboxylic acid (as atotal amount of adipic acid and terephthalic acid). The results areshown in Table 3 below.

TABLE 3 Generated amount of THF based on 1 Example mole of dicarboxylicacid (mol) Example 1 0.17 Example 2 0.22 Example 3 0.18 Example 4 0.15Example 5 0.25 Comparative Example 2* 1.09 *The amount of THF generatedin Comparative Example 2, provided for comparison with Examples 1 to 5,was calculated after an esterification reaction in a 3-necked glassflask in the same molar ratio of monomers and at the same reactiontemperature as those in Example 1 disclosed in Korean Publication No.10-2011-007186.

Referring to Table 3, the amounts of generated THFs in Examples 1 to 5were significantly lower than that of Comparative Example 2.

Evaluation Example 4 Color Comparison

Colors of the biodegradable PBATs prepared in Examples 1 to 3 andReference Examples 1 and 2 were measured using a colorimeter(SpectraMagic NXKonica Minolta) to obtain L-values and b-values andevaluate color characteristics. The results are shown in Table 4 below.

The nearer to 100, the L value as a whitening value indicates purewhite.

The b value, which is related with yellow and blue colors, indicatesyellow when it is a (+) value, and blue when it is a (−) value.Accordingly, the larger the L value, the brighter the color, and thenearer to 0 the b value is, the better the color characteristics.

TABLE 4 Example Color (L*/b*) Example 1 83.08/5.02 Example 2 84.35/4.13Example 3 82.35/4.22 Reference Example 1  75.77/11.89 Reference Example2 86.32/4.44

Referring to Table 4, the biodegradable PBAT of Reference Example 1 isfound to have a remarkably larger b value than those of thebiodegradable PBATs of Examples 1 to 3, indicating that colorcharacteristics of the biodegradable PBAT of Reference Example 1 weredeteriorated due to depolymerization by heat. Meanwhile, thebiodegradable PABT of Reference Example 2 was not significantlydifferent in color characteristics from the biodegradable PABTs ofExamples 1 to 3, since the second polycondensation reaction and thirdpolycondensation reaction in Reference Example 2 were not sufficient toinduce depolymerization known as a cause of color changes. However, asdescribed above in Evaluation Example 1, the intrinsic viscosities ofthe second polycondensation reaction product and the biodegradable PABTprepared in Reference Example 2 were too small than they should be forintended uses.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A continuous preparation method of a biodegradable aliphatic/aromaticpolyester copolymer, the method comprising: performing a firstesterification reaction of an aliphatic dihydroxy compound with analiphatic dicarboxylic acid at a temperature of 185° C. or less;continuously performing a second esterification reaction of a reactionproduct from the first esterification reaction; continuously performinga first polycondensation reaction of a reaction product from the secondesterification reaction to obtain a prepolymer; continuously performinga second polycondensation reaction of the prepolymer to obtain a secondpolycondensation reaction product having an intrinsic viscosity fromabout 0.9 dl/g to about 1.0 dl/g; and continuously performing a thirdpolycondensation reaction of the second polycondensation reactionproduct to prepare the biodegradable aliphatic/aromatic polyestercopolymer, wherein the performing of the first esterification reactionor the continuously performing of the second esterification reactioncomprises adding an aromatic carboxylic acid.
 2. The continuouspreparation method of claim 1, wherein the biodegradablealiphatic/aromatic polyester copolymer resulting from the thirdpolycondensation reaction has an intrinsic viscosity from about 1.4 dl/gto about 1.9 dl/g.
 3. The continuous preparation method of claim 1,wherein the first esterification reaction is performed at a temperatureof about 160° C. to about 185° C.
 4. The continuous preparation methodof claim 1, wherein the second esterification reaction is performed at atemperature of about 220° C. to about 250° C.
 5. The continuouspreparation method of claim 1, wherein an amount of the aliphaticdihydroxy compound is in a range of about 1.1 moles to about 1.5 molesbased on 1 mole of a total amount of the aliphatic dicarboxylic acid andthe aromatic dicarboxylic acid.
 6. The continuous preparation method ofclaim 1, wherein the second polycondensation reaction is performed at atemperature of about 220° C. to about 250° C., a degree of vacuum ofabout 2 torr to about 7 torr, and a reaction mixture residence time ofabout 1.5 hours to 3 hours.
 7. The continuous preparation method ofclaim 1, wherein the third polycondensation reaction is performed at atemperature of about 220° C. to about 250° C., a degree of vacuum ofabout 0.5 torr to about 2 torr, and a reaction mixture residence time ofabout 1 hour to 3 hours.
 8. The continuous preparation method of claim1, wherein the first polycondensation reaction is performed at atemperature of about 220° C. to about 250° C., a degree of vacuum ofabout 10 torr to about 50 torr, and a reaction mixture residence time ofabout 1.5 hours to 3 hours.
 9. The continuous preparation method ofclaim 1, wherein the first esterification reaction is performed in abatch reactor or is continuously performed in an esterification reactor.10. The continuous preparation method of claim 1, wherein the performingof the first esterification reaction of the aliphatic dihydroxy compoundwith the aliphatic dicarboxylic acid comprises adding at least oneselected from a catalyst, a heat stabilizer, a branching agent, a colorstabilizing agent, and a color control agent.
 11. The continuouspreparation method of claim 1, wherein the continuously performing ofthe first polycondensation reaction comprises adding a catalyst.